Over the years, the heavy-duty trucking market has adopted the diesel engine as its preferred power source due to both its excellent longevity and its economy of operation. Recently, the specifications for heavy-diesel engines indicate a longer interval between oil changes than has been customary in the past. For the user of commercial vehicles such as cross-country freight carriers, extended lubrication intervals (30,000 miles, 4.8×104 km, or more) mean more on-the-road time and a greater rate of return on the investment as well as decreased maintenance costs.
Specialized lubricants have been developed to meet the more stringent performance requirements of heavy-duty diesel engines compared to passenger car engines. Lubricating greases are employed in a wide range of applications where heavy pressures exist, including wheel bearing, chassis, steering drag links, king pins, transmission cross shaft spring pins, shackle pins, brake cam shafts, and fifth wheel faceplates and pivots operating under high and low temperature conditions.
Extended lubrication intervals using currently available greases have led to driver complaints of hard steering. Also, high wear has been observed on king pins, shackles, and ball and steering knuckle joints. The cause of high wear in these areas appeared to be due to salt corrosion. This salt corrosion caused deep pitting of the metal surfaces and also plugged lubrication ducts, thus accelerating wear due to the lack of lubrication. Currently available greases do not provide the necessary degree of rust protection of the lubricated parts for long service interval use.
In addition, greases with poor water wash-off or water repellency decrease the longevity of the grease and increase wear on the surface being lubricated. Greases which come in contact with water often harden and sometimes separate from the parts to be lubricated. In the hardened condition, these greases do not work their way back into the parts to be lubricated. Since the grease hardens and separates from the parts to be lubricated, it no longer seals out water, dirt or salt which can cause abrasive wear and rusting.
Another problem encountered with currently available greases is that they are not work-stable. In other words, they do not stay put on the lubricated parts, thus leaving the parts without lubrication, and allowing for only short service intervals before the grease must be replenished. Currently available greases also tend to be displaced under shock loading conditions. Shock loading conditions to the entire steering system can occur, for example, when a wheel hits a bump in the road. The sudden shock tends to force the lubricated parts together, squeezing the grease out from between them. On a commercial vehicle, one such point subject to shock loading is the fifth wheel. If a severe bump is hit, shock loading can occur, leading to subsequent binding of this pivot point.
A grease which will meet the requirements for extended lubrication intervals for such vehicles must not only have the above described characteristics, but must also have appropriate high and low temperature properties. In other words, the grease should not soften and run under operating conditions encountered in warmer climates, and yet, should as well exhibit good low temperature pumpability in colder climates.
Due to ever increasing demands for higher performance, it would be desirable to provide greases which exhibit improved lubrication properties, and in particular, improved water protection performance and wear protection performance along with increased grease lifetime.